Field of the Invention
The present invention relates to an optical system and an optical quality measuring apparatus.
Description of the Related Art
Feeling of gloss (feeling of glossiness, optical quality) of an object such as printed matters, coatings, and plastic materials is an important factor for quality of the object. There have been conventionally various indexes according to characteristics of a surface to be detected serving as a concrete value representing the feeling of gloss, and measuring methods for the indexes. For example, these indexes comprise specular glossiness, haze and image clarity, spectral characteristics and the like. Japanese Patent Laid-Open No. 2001-41888 discloses a method for estimating and determining feeling of gloss by combining indexes measured by a plurality of mutually differing light-receiving angles in order to reduce difference between the glossiness serving as a value representing the feeling of gloss and the feeling of gloss actually felt by sight.
However, the method disclosed by Japanese Patent Laid-Open No. 2001-41888 uses photodetectors different from each other depending on each of the plurality of light-receiving angles. Therefore, the method disclosed by Japanese Patent Laid-Open No. 2001-41888 increases the provided number of the photodetectors by increasing the variation of the light-receiving angles in order to improve precision (accuracy) of the glossiness, and causes the configuration of an optical system to become complicated. In contrast, a conventional optical system exists in which the configuration is simplified by using the common photodetector to a plurality of measurements with the plurality of light-receiving angles. However, in the optical system using the shared photodetector, light irradiated at the measurement with one light-receiving angle can enter an optical path used in the measurement with another light-receiving angle to output a signal with noise by the photodetector.